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28 

ObservAir

 Operating Manual 

 

We  recognize  that  regulatory  monitoring  stations  with  open  data 

access  may  not  be  available  in  many  areas.  Span  calibration  of  the 
ObservAir is a highly involved process that requires specialized equipment. 
Some  basic  validation  procedures  may  be  added  to  this  manual  in  the 
future, but for the moment, please contact 

[email protected]

 to inquire about 

our calibration services.  
 

4.3.

 

 Flow rate calibration 

 
The  flow  rate  sensor  is  calibrated  at  DST  prior  to  shipment,  but  sensor 
output  may  drift  over  long  periods  (weeks  or  months  of  operation)  and 
should be re-calibrated periodically using the instructions below: 
 
1.

 

Turn on the ObservAir and allow it to warm-up for at least 15 minutes.  

2.

 

Connect ObservAir to a serial monitor (Section 3.6). 

3.

 

Set the ObservAir to the desired flow rate setting using the appropriate 
serial command. 

4.

 

Connect  a  primary  flow  calibrator,  such  as  a  Gilian  Gilibrator,  to  the 
ObservAir’s inlet such that the sensor’s intake flow is measured.  

5.

 

Collect at least 5 flow rate measurements using the calibrator. The flow 
rate  measurements  should  not  vary  by  more  than  ±1  ccm.  Take  the 
average  of  all  calibrator  measurements:  this  is  the  reference  value 
(

FR

ref

). 

6.

 

From the serial output, collect at least 5 flow rate measurements from 
the ObservAir and take the average: this is the measured value (

FR

m

). 

7.

 

Calculate the calibration factor: 

FR

cal

 = 

FR

ref

/FR

m

 

8.

 

Update  the  sensor’s  FRcal  factor  using  the  serial  command  (Section 
3.6.3).  

9.

 

Repeat Steps 5 and 6 until the reference and measured values agree 
within 2 ccm.  

 
If a primary flow calibrator is not available, another flow rate sensor may be 
used,  but  clearly  the  calibration  is  only  as  good  as  the  reference 
measurements collected.  
 

4.4.

 

Leak check  

 
The ObservAir incorporates a monolithic design architecture that is more 
robust  than  traditional  instruments  and  less  susceptible  to  leakage. 
However, it is best practice to periodically check the integrity of the closed 
flow path using the instructions below:  
 

 

 

29 

ObservAir

®

 Operating Manual 

1.

 

Turn off the ObservAir 

2.

 

Replace the filter 

3.

 

Plug the ObservAir’s exhaust port. A simple plug may be fashioned by 
tying a knot in a length of sample line (soft rubber tubing).  

4.

 

Connect a vacuum gun (e.g. a MityVac) to the inlet nozzle using a length 
of  sample  line.  The  vacuum  gun  must  be  outfitted  with  a  pressure 
gauge.  

5.

 

Pump the gun until you achieve a vacuum pressure of –10 inch of H

2

O. 

Note that the pressure may ‘bounce back’ after every pump – this is 
normal and is a result of the filter’s flow resistance.  

6.

 

Monitor  the  vacuum  pressure  for  about  1  minute  to  ensure  that  it 
remains  constant  (the  sensor  is  holding  vacuum,  and  therefore  not 
leaking). The vacuum pressure may drop by up to –1 inch of H

2

O over 

60 seconds. If the sensor meets or exceeds this criterium, it has passed 
the leak check and may be deployed.  

7.

 

If the sensor fails the leak check, first tighten the thumbscrew by 1 full 
turn and repeat steps 5 and 6.  

8.

 

If the sensor still fails, replace the filter and repeat steps 5 to 7.  

9.

 

If the sensor fails after these attempts, contact DST Technical support 
at 

[email protected]

  (please  include  the  unit(s)  serial  numbers  in  the 

subject line).  

 

Note: 

The ObservAir’s micropump can achieve a static vacuum pressure of 

~2  inch  of  H

2

O  and  operates  at  <<  1  inch  of  H

2

O  when  monitoring  air 

pollution. Therefore, some small vacuum loss is allowed at the –10  inch of 
H

2

O setpoint, as this will not result in any perceptible leakage during normal 

operation.  

 

 

Содержание ObservAir

Страница 1: ...rational limits and warnings 11 3 Operating Instructions 13 3 1 Hardware overview 13 3 2 Interactive LED button Sensor display and control 14 3 2 1 Sensor startup 15 3 2 2 Default LED mode Pollutant c...

Страница 2: ...pport WiFi and USB communication protocols and include a 16GB removable SD card for onboard data storage Units may also be supplemented with an LTE LoRa or SigFox communication module and a GPS unit f...

Страница 3: ...collection area is 3 mm in diameter After the first filter the air flow passes through a second reference filter assembly that is identical to the first Since the air is filtered devoid of PM the int...

Страница 4: ...plication Operate the 7 ObservAir Operating Manual ObservAir for 12 to 24 hours in an environment that is free of the analyte gas es and average the voltage differential data collected over the entire...

Страница 5: ...technical specifications are summarized in the tables below All electrochemical cells are sourced from Spec Sensors Gas measurement performance specifications are adapted from data provided by the ma...

Страница 6: ...intervals 2 3 Operational limits and warnings Environmental limits Only operate the ObservAir within the conditions listed in Table 1 Temperature and relative humidity must remain between 5 to 40 C an...

Страница 7: ...nd may result in permanent damage to the unit and or harm to the user Please contact DST Technical Support at info dstech io regarding any problems with your unit that cannot be resolved with the inst...

Страница 8: ...llutants For every new start up event a new data file is created on the SD card txt file and is assigned a filename that contains the sensor s ID number and the start up time date Section 3 5 1 3 2 2...

Страница 9: ...f the ObservAir hold the LED button to cycle through the menu until the first red flash and release The sensor will flash red two more times to confirm that it is shutting down 3 2 6 Sensor alarms and...

Страница 10: ...ront panel 19 ObservAir Operating Manual 3 5 Data collection from onboard SD card While the ObservAir is operating data is written to the onboard SD card in real time as both a primary means of data c...

Страница 11: ...e ADC s raw count Full scale value is 8388607 d ATN Optical attenuation unitless e BC Black carbon in g m3 f T Temperature in C g RH Relative humidity in h FR Sample flow rate in ccm i VBAT Battery vo...

Страница 12: ...tings Figure 12 6 With the Serial Monitor configured ObservAir data is displayed in real time at the time interval set by the user Commands can also be sent to the sensor using the dialog box at the t...

Страница 13: ...8 to 1 2 Set flow rate calibration coefficient Table 7 ObservAir serial commands and descriptions 25 ObservAir Operating Manual 3 7 WiFi connection Provisioning WiFi credentials to the ObservAir allo...

Страница 14: ...1 Zero calibration of pollution sensors Each ObservAir comes with a zero calibration sheet but it is good practice to periodically verify the sensor s baseline performance especially before and after...

Страница 15: ...but clearly the calibration is only as good as the reference measurements collected 4 4 Leak check The ObservAir incorporates a monolithic design architecture that is more robust than traditional ins...

Страница 16: ...loading artifact is not static it depends on the emissions source e g biomass vs diesel atmospheric conditions seasonality and other factors Therefore filter loading correction algorithms should be c...

Страница 17: ...ing can be optimized to meet your needs For example if greater BC measurement resolution is desired at the expense of filter life the flow rate can be increased past the minimum value Conversely flow...

Страница 18: ...exhaust stacks vehicle tailpipes and other pollution sources When sampling emissions directly do not exceed the ObservAir s maximum temperature relative humidity range and pollution concentration rat...

Страница 19: ...If BC measurements are proportionally lower than the reference value then it is also possible but less likely that the ObservAir is leaking Given these potential error modes it is important to valida...

Страница 20: ...38 ObservAir Operating Manual Figure 14 Hard reset using the magnetic cover...

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